A study suggesting that organic agriculture gives better pest control and larger plants than conventional farming is sure to reignite longstanding debates about the merits of organic versus conventional agriculture. It also highlights an often-neglected aspect of biodiversity.

"Organic agriculture promotes more balanced communities of predators," says David Crowder, author of the new study published today in Nature.

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"Our study does not tell farmers they should shift to organic agriculture. What our study suggests is that organic agriculture is promoting these more balanced natural enemy communities and they may have better, organic pest control."

Much focus is put on species numbers or 'richness'. But the research by Crowder, an insect ecologist at Washington State University in Pullman, and his colleagues, shows the importance of 'evenness' — the relative abundance of different species. Evenness quantifies not just the presence of different species, but whether one is dominant or whether there is an equal distribution of numbers between species.

The team looked at the bugs, nematodes and fungi that attack the hated Colorado potato beetle (Leptinotarsa decemlineata).